Kin Recognition and Human Facial Resemblance

Why Recognize Kin? Mate Choice (avoid inbreeding) Mate Choice (avoid inbreeding) Inclusive Fitness (favour kin) Inclusive Fitness (favour kin)

Relatives other than your direct offspring can share your genes. Helping them to reproduce can increase your own fitness. If organisms do show differential treatment to kin according to the degree of relatedness, how do they detect kinship? Relatives other than your direct offspring can share your genes. Helping them to reproduce can increase your own fitness. If organisms do show differential treatment to kin according to the degree of relatedness, how do they detect kinship? Inclusive Fitness Theory

Base Participant Creating Resemblance Morph Intermediate Template Intermediate Template

non-self morph self morph non-self morph Morphs Participants

Are people more likely to trust others with faces that resemble their own?

The Trust Game P2 DeBruine (2004) Proc Roy Soc Lond B

Average Number (out of 3) Effect of Resemblance on Game Behaviour DeBruine (2002) Proc Roy Soc Lond B

Average Female Participant Transforming Faces

Subject Average Male Average Male Transform Transforms Base Face Base Face - - X X = = ( ( ) ) Endpoint Faces

Transformed Stimuli Subject Same-Sex Transform Same-Sex Transform Other-Sex Transform Other-Sex Transform

Do people find faces similar to their own more attractive? Is this different for same- sex and other-sex faces?

Click on the face you find more attractive.

Attractiveness Difference Score Resemblance Increases “Attractiveness” DeBruine (2004) Proc Roy Soc Lond B

Averageness Difference Score Resemblance Increases “Averageness” DeBruine (2004) Proc Roy Soc Lond B

Context-Specificity Cues of kinship should cause context-specific effects that increase prosocial behaviour and attributions 2. decrease attractiveness for mating Within the domain of mating, cues of kinship should be more aversive in the context of a short-term relationship than a long-term relationship. Cues of kinship should cause context-specific effects that increase prosocial behaviour and attributions 2. decrease attractiveness for mating Within the domain of mating, cues of kinship should be more aversive in the context of a short-term relationship than a long-term relationship. DeBruine (2005) Proc Roy Soc Lond B

Average Difference Score Context-Specific Effects

What causes individual differences in preferences for self-resemblance?

Menstrual Cycle Effects Average Self-Preference Score DeBruine, Jones & Perrett (2005) Hormones & Behavior

Hormonal Correlates Day of menstrual cycle (n=71) Self-resemblance preference Fertility risk Estrone glucuronide (mmol/L/24h) Estimated Estrogen Pregnanediol glucuronide (umol/L/24h) Estimated Progesterone DeBruine, Jones & Perrett (2005) Hormones & Behavior

Are there sex differences in how much people prefr self-resemblance in children’s faces?

Which of these children would you be most likely to adopt?

Platek vs. DeBruine Morphing Methods Original Changed Child Morph DeBruine (2004) Evolution & Human Behavior

Platek vs. DeBruine Results Platek found that men preferred self-resemblance more than women, who still significantly preferred self-resemblance DeBruine found that men and women preferred self- resemblance equally (Others could match the child faces made using both DeBruine and Platek methods equally well to the adult faces they were made from, and slightly more accurately for female adult faces than male adult faces) Platek found that men preferred self-resemblance more than women, who still significantly preferred self-resemblance DeBruine found that men and women preferred self- resemblance equally (Others could match the child faces made using both DeBruine and Platek methods equally well to the adult faces they were made from, and slightly more accurately for female adult faces than male adult faces)

Facial Self-Resemblance 1. Increases trustworthiness (both behaviours and attributions) 2. Increases the attractiveness of same-sex faces more than other-sex faces 3. Has different effects in mating and prosocial contexts 4. Is affected by hormones across the menstrual cycle 5. May or may not be evaluated differently by by men and women in the context of children’s faces